The U.S. President during the Louisiana Purchase, which occurred in 1803, was Thomas Jefferson. As a proponent of westward expansion, Jefferson saw the acquisition of the territory as essential to the growth of the United States. The purchase involved land stretching from the Mississippi River to the Rocky Mountains, effectively doubling the size of the nation at that time. It provided a vital opportunity for exploration and settlement, allowing for increased agrarian development and fulfilling the vision of "Manifest Destiny." Jefferson’s administration negotiated the deal with France, then led by Napoleon Bonaparte, which significantly impacted U.S. history.